Scientists believe quasars are powered by gas and dust falling into enormous black holes at the heart of some galaxies.

About a hundred thousand quasars are known, of which only about a hundred are believed to be binaries—an orbiting pair of supermassive black holes that come together when two galaxies collide and merge.

"Binaries are rare. This is the first triple," George Djorgovski, an astronomy professor at the California Institute of Technology in Pasadena, said yesterday at a meeting of the American Astronomical Society in Seattle, Washington.

The three quasars are 10.5 billion light-years away from Earth, but are only a hundred thousand light-years apart from each other.

Because light from the quasars has been in transit for billions of years, looking at them is also peering backward into the universe's distant past, astronomers note.

Scientists also expect the discovery to reveal the new and potentially violent ways that three quasars in close quarters might interact.

Statistical Impossibility

Most galaxies, including the Milky Way, are thought to have supermassive black holes at their centers, but not all such black holes are quasars.